/Engine/Source/Runtime/Engine/Classes/Engine/Engine.h
Prepares the engine for a map change by pre-loading level packages in the background.
true if all packages were in the package file cache and the operation succeeded, false otherwise. false as a return value also indicates that the code has given up.
bool PrepareMapChange ( [FWorldContext](API\Runtime\Engine\Engine\FWorldContext) & WorldContext, const [TArray](API\Runtime\Core\Containers\TArray)< [FName](API\Runtime\Core\UObject\FName) > & LevelNames )